1. Field of the Invention
The present invention relates to an optical recording/reproducing method and apparatus that records information onto or reproduces information from a storage medium, such as an optical disk, by focusing a light beam, emitted by a light source, onto a recording layer of the storage medium.
2. Description of the Related Art
Recently, there are various optical storage media that are provided for recording and reproducing of information, including CD-DA, CD-ROM, CD-R (compact disk recordable), DVD-ROM, DVD-R (digital versatile disk recordable), etc.
Japanese Laid-Open Patent Application No. 11-134691 discloses an optical recording/reproducing method which determines an optimum recording power based on a relationship between the modulation parameters and the recording powers. In this method, a test writing is first performed in which writing a pattern of marks and spaces to an optical storage medium with a recording power is repeated by sequentially changing the recording power with increments. A test reading is next performed in which reading the pattern from the storage medium is repeated, so that data signals are reproduced from the respective patterns on the storage medium. A modulation parameter is then calculated for each of the reproduced data signals, each modulation parameter corresponding to one of the respective recording powers. Then, an optimum recording power is determined based on the relationship between the modulation parameters and the recording powers.
However, in the optical recording/reproducing method of the above document, the algorithm to determine the optimum recording power is inadequate for accurately checking the rising slope of the modulation parameter related to the reproduced data signal. In the optical recording/reproducing method of the above document, variations of the optimum recording power may be produced due to inaccurate checking of the rising slope of the modulation parameter.
Generally, the effective range of the write power, which is supplied to the laser diode, that the laser beam emitted by the laser diode and focused on the storage medium starts forming a mark on the storage medium is very narrow. On the other hand, the locations of the storage medium to which the test patterns are written are limited, and an increase of the amount of increments to the write power level or an increase of the number of the cycles of the test writing/reading will not be an appropriate solution to the problem of inaccurate checking of the rising slope of the modulation parameter.
For example, the recording power is sequentially changed with increments of 1.0 mW from 10.0 mW to 19.0 mW, which falls within a range of ±30% centered around 15.0 mW. In this case, the test writing is repeated ten times by sequentially changing the recording power with such increments.
In a case of CD-RW media, a phase-change recording material is used in the recording layer of the optical disk. The effective range of write power supplied to the laser diode that enables the emitted laser beam focused on the disk to form a mark on the storage medium is very narrow. If the write power is increased by 1 or 2 mW, the amplitude of the reproduced data signal becomes considerably large. Specifically, even if the reproduced signal amplitude is about 0.1 (noise level) at the write power p=14 mW, the reproduced signal amplitude abruptly rises to a high level of 0.5 to 1.4 at the write power p=15 mW that is incremented from 14 mW.
Accordingly, it is desirable that the algorithm to determine the optimum recording power includes a data selection procedure for accurately checking the rising slope of the modulation parameter related to the reproduced data signal. As described above, if the checking of the rising slope of the modulation parameter related to the reproduced data signal is inaccurate, variations of the optimum recording power may be produced.